Forward emission of positronium from nanochanneled silicon membranes

Abstract

Positronium beam formation and manipulation are required in several fundamental experiments. Efficient positron/positronium conversion in transmission configuration would offer important geometrical advantages over the reflection one for these applications. A novel type of transmission positron/positronium converters, which consists of silicon membranes with pass-through nanochannels, was produced and tested. The amount of forward emitted positronium was studied as a function of the thickness of the membranes and the nanochannel size. A maximum of, at least, $(16\ifmmode\pm\else\textpm\fi{}4)%$ of positrons implanted in $(3.5\ifmmode\pm\else\textpm\fi{}0.5)\ensuremath{-}\ensuremath{\mu}\mathrm{m}$-thick membrane with a nanochannel size of 5--8 nm were found to be forward emitted as positronium. A similar maximum amount of, at least, $(16\ifmmode\pm\else\textpm\fi{}5)%$, was found to be emitted from a membrane $(7.7\ifmmode\pm\else\textpm\fi{}1.3)\ensuremath{-}\ensuremath{\mu}\mathrm{m}$-thick with a nanochannel size of 7--10 nm. A preliminary evaluation shows that the maximum amount of forward emitted positronium with the entire kinetic energy distribution below 1 eV is, at least, 9% of the positrons implanted in the $(3.5\ifmmode\pm\else\textpm\fi{}0.5)\ensuremath{-}\ensuremath{\mu}\mathrm{m}$-thick membrane.